1. Field of the Invention
The present invention relates to a substrate holder for use in a plating apparatus for plating a to-be-plated surface of a substrate, especially to form a plated film in fine trenches for interconnection, holes, and resist openings in the surface of a semiconductor wafer, or to produce bumps (protrusive electrodes) on the surface of a semiconductor wafer for electric connection to package electrodes or the like, a plating apparatus having such a substrate holder, and a plating method using such a substrate holder.
2. Description of the Related Art
In a TAB (Tape Automated Bonding) and a flip chip, for example, protrusive connection electrodes (bumps) of gold, copper, solder, or nickel, or layers thereof are formed at predetermined locations (electrodes) on the surface of a semiconductor chip with interconnections formed thereon, and the semiconductor chip is electrically connected to package electrodes or TAB electrodes by those bumps. There are various methods for forming these bumps, including electroplating method, vapor deposition method, printing method, and ball bump method. As the number of I/O terminals on semiconductor chips increases and the pitch thereof decreases, the electroplating method is finding more use in forming bumps because it can produce smaller bumps and provide relatively stable performance.
The electroplating method is available in different types in the art. One of those different electroplating methods is a spurting or cup method wherein a surface to be plated of a substrate, such as a semiconductor wafer or the like, is horizontally placed so as to face downwardly, and a plating solution is spurted from below. The other method is known as a dipping method wherein a substrate to be plated is vertically erected in a plating tank and a plating solution is introduced upwardly into the plating tank so as to overflow the plating tank when the substrate is dipped and plated in the plating solution flowing in the plating tank. The dipping method is advantageous in that it allows bubbles that would adversely affect the quality of the plated film to be easily removed, and the footprint is small. The dipping method is therefore considered to be suited for the bump plating in which holes to be filled by the plating are relatively large and which requires a fairly long plating time.
When using the dipping-type electroplating apparatus to form the bump, the air bubbles can escape easily. Conventional electroplating apparatus for carrying out the dipping method have a substrate holder for detachably holding a substrate, such as a semiconductor wafer or the like, while sealing its outer circumferential edge and reverse side, and exposing its surface to be plated. The substrate holder with the substrate held thereby is dipped in a plating solution to plate the surface of the substrate.
The substrate holder is required to reliably seal the outer circumferential edge of the substrate for preventing the plating solution from going therearound to the reverse side of the substrate when the substrate holder holds the substrate. One known substrate holder has a pair of openable and closable supports (holding members) with a presser ring mounted on one of the supports. When the substrate is positioned between the supports, a rotary ring is rotated to press one of the supports toward the other, pressing a seal ring fixed to one of the supports against the outer circumferential edge of the substrate, thereby to seal the outer circumferential edge of the substrate and hold the substrate.
With the above conventional substrate holder, when the presser ring is rotated, one of the supports is pressed toward the other to hold the substrate. Upon rotation of the presser ring, the support is deformed, straining the seal ring which finds it considerably difficult to fully seal the outer circumferential edge of the substrate. Especially, when a plated film is to be embedded in fine recesses defined in the surface of the substrate, it is the general practice to use a highly permeative plating solution which can easily and reliably find its way into the fine recesses. Therefore, the use of such a highly permeative plating solution makes it more difficult to completely seal the outer circumferential edge of the substrate.
For successively plating a substrate and processing the substrate in connection with the plating process, it has been customary in the art to hold the substrate with a substrate holder and move the substrate holder with a transfer device successively through plating and processing tanks wherein the substrate held by the substrate holder is dipped in the plating solution and processing liquids.
If a small lot of substrate products are to be manufactured, and the substrate is held by the substrate holder and delivered to and processed by the processing tanks, then the transfer device tends to be large in size, and a substrate loading/unloading device is required for horizontally loading and unloading the substrate. As a result, the overall plating apparatus is likely to be large in size.